With hot, dry winds, the question came up this week about whether the hot temperatures or the low humidity would affect pollen viability. It turns out that both day and night time temperatures will affect pollen tube growth. That in ‘Hass' approximately 48 hours about 50 deg F is needed to complete pollen tube growth and fertilization. If temperatures drop at night to below 50, there's not enough time for fertilization to occur. As temperatures increase, fertilization occurs more easily. In the tropics, there can be high temperatures and high humidities and good fruit set. But this question was not about fertilization, but how long the pollen would remain viable at high temperatures and low humidities. Work was done Loupassaki and Vasilakis for the World Avocado Congress III Proceedings and they basically found that when humidity dropped below 40%, viability was very low. This last week we have seen humidities below 10%. It probably means that even with bee visitation, non-viable pollen is being delivered to the flowers. When humidities come back up, there will probably be good fertilization, as long as we have decent day and night time temperatures.
Many years ago Gary Bender, down in San Diego, went to the Gulf Region of the Middle East to help establish an avocado orchard. The trees flowered, but never set fruit.
